Added proper extension manifest parser for launcher_page.
Previously, AppListViewDelegate manually parsed the manifest. We now
have a proper parser class that generates appropriate errors for invalid
launcher_page fields in a manifest, with full valid and invalid unit
tests.
BUG=
399131
Committed:
https://crrev.com/2be0d05247cc0f2f236540bd19b62a41896dd2ae
Cr-Commit-Position: refs/heads/master@{#291856}